Lyme disease, caused by the spirochetal bacterium Borrelia burgdorferi, is the most prevalent arthropod-borne disease in the United States and Europe. Although early stage Lyme disease often can be treated with antibiotics, if left untreated, the disease can progress to become a devastating chronic illness, most frequently characterized by heart block, peripheral neuropathies, and migratory arthritis. Although it has been over 20 years since B. burgdorferi was first isolated, there is still much progress to be made towards understanding the contributions of B. burgdorferi‘s individual genes to issues of tick colonization (maintenance in the environment), mammalian infectivity (ability to infect human skin), and pathogenicity (tissue dissemination and chronic infection).

The zoonotic life cycle of B. burgdorferi is complex, involving both an arthropod tick (Ixodes scapularis) vector and a mammalian host. The ability of B. burgdorferi to occupy these two very diverse niches is governed by a complex regulatory shift that dramatically alters the expression of several major outer surface proteins. One of the most important findings in the area of B. burgdorferi pathogenesis research was the identification of the Rrp2/RpoN/RpoS alternative sigma factor cascade. Mutational experiments have confirmed that this regulatory network is required for the aforementioned regulatory shift and vital for both vector-to-host transmission and establishing an infection in the mammal. Although subsequent experimentation has identified several Rrp2/RpoN/RpoS-regulated major outer surface lipoproteins (e.g. OspC and DbpA) that are partially responsible for the attenuated pathogenic phenotype exhibited by the B. burgdorferi mutant lacking this regulatory network, transcriptional microarray analyses carried out on this same mutant strain indicate that the impact of the Rrp2/RpoN/RpoS regulatory pathway extends far beyond just these two outer surface proteins. Therefore, additional work is required identify and characterize other genes within this regulon that might potentially play a role in the infectious life cycle of B. burgdorferi.

Given that B. burgdorferi has been exceedingly refractory to methods typically used to genetically manipulate other bacteria, the need for new genetic approaches for manipulation, regulatory studies, and mutational analysis are paramount. To this end, significant emphasis has been placed on developing new techniques for the genetic analysis and genetic manipulation of the spirochete. I have successfully adapted a controllable/inducible gene expression system, which expresses a desired gene in a switch-like manner, and a new gene expression reporter for studying gene regulation in the Lyme disease spirochete. Application of these two systems should help garner new information about how virulence expression is regulated in B. burgdorferi and, ultimately, help to break open studies on many aspects of Lyme disease pathogenesis and chronicity.